Self piercing rivets and associated tools for fastening two or more pieces of material with respect to one another are generally known. See U.S. Pat. No. 5,752,305: U.S. Pat. No. 5,779,127; U.S. Pat. No. 5,813,114; U.S. Pat. No. 5,884,386; U.S. Pat. No. 6,089,437; and U.S. Pat. No. 6,116,835. Self piercing rivets have typically been used in non critical connections attaching two or more pieces of material with respect to one another.